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  2. North American Industry Classification System - Wikipedia

    en.wikipedia.org/wiki/North_American_Industry...

    It has largely replaced the older Standard Industrial Classification (SIC) system, except in some government agencies, such as the U.S. Securities and Exchange Commission (SEC). An establishment is typically a single physical location, though administratively distinct operations at a single location may be treated as separate establishments.

  3. Telephone exchange names - Wikipedia

    en.wikipedia.org/wiki/Telephone_exchange_names

    Telephone numbers listed in 1920 in New York City having three-letter exchange prefixes. In the United States, the most-populous cities, such as New York City, Philadelphia, Boston, and Chicago, initially implemented dial service with telephone numbers consisting of three letters and four digits (3L-4N) according to a system developed by W. G. Blauvelt of AT&T in 1917. [1]

  4. All-number calling - Wikipedia

    en.wikipedia.org/wiki/All-Number_Calling

    The first two or three letters of the exchange name translated into digits given by a mapping typically displayed on the telephone's rotary dial by grouping the letters around the associated digit. The table (right) shows the typical assignment in the Bell System in use at the time. The letter Q was not used, and Z was translated to 0 (zero) on ...

  5. Telephone numbers in Canada - Wikipedia

    en.wikipedia.org/wiki/Telephone_numbers_in_Canada

    Telephone numbers in Canada follow the fixed-length format of the North American Numbering Plan (NANP) of a three-digit area code, a three-digit central office code (or exchange code), and a four-digit station or line code. This is represented as NPA NXX XXXX. [1]

  6. Director telephone system - Wikipedia

    en.wikipedia.org/wiki/Director_telephone_system

    In a Director area there were 8 digits available for the A-digit letter of the exchange name (excluding ‘1’and ‘0’), and 9 digits each for the B-digit and C-digit letters; hence there were a maximum of 648 exchange names (8 × 9 × 9), though in practice some ABC codes (e.g. 555) did not have a usable name equivalent, and by 1966 London ...

  7. Interchangeable NPA and central office codes - Wikipedia

    en.wikipedia.org/wiki/Interchangeable_NPA_and...

    The ten-digit telephone numbers of the North American Numbering Plan consist of a three-digit numbering plan area code (NPA code), written as the most-significant part of the national telephone number, followed by the three-digit central office code, and the four-digit local line or station number.

  8. Data Universal Numbering System - Wikipedia

    en.wikipedia.org/wiki/Data_Universal_Numbering...

    From October 2003 [5] to April 2022 [6] the United States government required that all organizations doing business with the federal government use a DUNS number as an identifier. After April 4, 2022, the federal government instead began using the Unique Entity ID created in SAM.gov .

  9. Telephone prefix - Wikipedia

    en.wikipedia.org/wiki/Telephone_prefix

    A telephone prefix is the first set of digits after the country, and area codes of a telephone number. In the North American Numbering Plan countries (country code 1), it is the first three digits of a seven-digit local phone number, the second three digits of the 3-3-4 scheme. In other countries, both the prefix and the number may have ...